Permanganate [Mn(VII)] has gained
broad attention in
water treatment.
However, its limited reactivity toward some refractory micropollutants
hinders its application for micropollutant degradation. Herein, we
introduced UVA-LED photolysis of Mn(VII) (UVA-LED/Mn(VII)) to degrade
micropollutants (diclofenac (DCF), 4-chlorophenol (4-CP), atrazine,
and nitrobenzene) by selecting DCF and 4-CP as target micropollutants.
The effects of operating conditions (e.g., light intensity, radiation
wavelengths, pH, and water constituents) on DCF and 4-CP degradation
as well as the underlying mechanisms were systematically studied.
The degradation rates of DCF and 4-CP linearly decreased with increasing
radiation wavelengths (from 365 to 405 nm), likely due to the decreased
molar absorption coefficients and quantum yields of Mn(VII). Reactive
manganese species (RMnS), including Mn(V), Mn(III), and HO•,
were generated in the UVA-LED/Mn(VII) process. Mn(V) and HO•
were responsible for DCF degradation, while Mn(III), HO•, and
likely Mn(V) accounted for 4-CP degradation. Competitive kinetic results
revealed that contributions of RMnS and HO• decreased with
increasing radiation wavelengths, wherein RMnS played the dominant
role. Increasing pH displayed opposite effects on DCF and 4-CP degradation
with higher degradation efficiency obtained at acidic pH for the former
one but alkaline pH for the latter one. The presence of water background
ions (e.g., Cl–, HCO3
–, and Ca2+) barely influenced DCF and 4-CP degradation.
Finally, in comparison with Mn(VII) alone, enhanced degradation of
DCF and 4-CP by UVA-LED/Mn(VII) was observed in real waters. This
work advances the understanding of the photochemistry of manganese
species in micropollutant degradation and facilitates Mn(VII) oxidation
in practical application.